Optical systems are part of everyday life. The optical systems are found in virtually everywhere including in small portable electronics (e.g. digital camera, camcorder, camera phone, webcam), office supplies (e.g. printer, scanner, fax machine), surveillance systems, toys, quality control systems, laboratory and observatory equipments (e.g. telescope, microscope), medical equipments (e.g. endoscope), etc. The conventional lenses used in the optical systems continually face challenge of balancing image quality and production cost. The spherical lenses are widely used since they can be relatively easily fabricated with low cost. The optical systems using them, however, tend to suffer from the aberration problem and in turn produce low quality images. A sort of aspherical lenses configured to remove or reduce aberration can be used for improving image quality. However, the fabricating process of aspherical lenses is time consuming, complicated, and expensive, which hinder the wide use of the aspherical lenses.
Another challenge in the conventional lenses is to make them large. Conventional Fresnel type lenses are a good solution to make large lenses without handling large and heavy materials. However, the image quality of the Fresnel lens is not as good as that of the conventional lens.
To overcome the difficulties in fabricating conventional lenses, lenses using new fabrication methods have been introduced. Gradient index lenses are one example. Instead of using geometrical variation, the variation of refractive index is used to give the same effect in making a lens. Using the refractive index of material and geometrical variation together, the aberration of the optical system can be reduced. Although the gradient index lens gives the significant reduction of the aberration, it is still expensive and difficult to fabricate.
With the rapid growth of the MEMS technology, wide variety MEMS applications have been developed. One of well known application of the MEMS technology is micromirror devices using a plurality of micromirrors; for example, Digital Micromirror Device (DMD) used in the DLP (Digital Light Processing) projection devices. The DMD is an array of several hundred thousand micromirrors, wherein each individual micromirror has the same structure with one another and works as an on-off optical switch. With the success of the DMD technology, many efforts have been made to improve the micromirror devices to provide more advanced features such as multiple step motions, multiple degree of freedom motion, and simple actuation mechanism.
These advance features can be advantageously used to overcome the difficulties in fabricating conventional lenses. One exemplary micromirror device using these features is a Micromirror Array Lens reproducing conventional lenses. The Micromirror Array Lens comprises a plurality of micromirrors configured to have multiple step motions in multiple degrees of freedom and forms at least one optical surface profile by controlling the motions of the micromirrors. Each optical surface profile of the Micromirror Array Lens reproduces a conventional lens. The Micromirror Array Lens can be used as a variable focal length lens having multiple optical surface profiles. The Micromirror Array Lens with variable focal length lens and the properties of the Micromirror Array Lens can be found in U.S. Pat. No. 6,970,284 issued Nov. 29, 2005 to Kim, U.S. Pat. No. 7,031,046 issued Apr. 18, 2006 to Kim, U.S. Pat. No. 6,934,072 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 6,934,073 issued Aug. 23, 2005 to Kim, U.S. Pat. No. 7,161,729 issued Jan. 9, 2007 to Kim, U.S. Pat. No. 6,999,226 issued Feb. 14, 2006 to Kim, U.S. Pat. No. 7,095,548 issued Aug. 22, 2006 to Cho, U.S. Pat. No. 7,239,438 issued Jul. 3, 2007 to Cho, U.S. Pat. No. 7,267,447 issued Sep. 11, 2007 to Kim, U.S. Pat. No. 7,274,517 issued Sep. 25, 2007 to Cho, U.S. patent application Ser. No. 11/426,565 filed Jun. 26, 2006, U.S. patent application Ser. No. 11/743,664 filed May 2, 2007, and U.S. patent application Ser. No. 11/933,105 filed Oct. 31, 2007, all of which are incorporated herein by references. Typically, the micromirrors in the Micromirror Array Lens have the same structures with one another, wherein the structure is configured to provide a micromirror with multiple step motions. This structure is favorable when the Micromirror Array Lens reproduces multiple conventional lenses or a variable focal length lens.
Instead of producing multiple optical surface profiles, the Micromirror Array Lens can be configured to reproduce a single conventional lens or a fixed focal length lens as well. Each micromirror has a required motion to form a given optical surface profile but the required motion for one micromirror can be different from the required motions of others. When each micromirror is made to have the same structure, the structure still has to be configured to provide each micromirror with multiple motions just like the case of reproducing a variable focal length lens because each micromirror has a different required position. This can make the Micromirror Array Lens have unnecessarily complicated structure and require a control circuitry to control the motions of the micromirrors. In order to simplify the fabrication process and operation, the structure of the micromirror can be customized to have only the required motion.
The fixed focal length Micromirror Array Lens has a lot of advantages and can solve many problems in fabricating the conventional lenses. First, the fabrication process of the Micromirror Array Lens is size independent. Since the Micromirror Array Lens uses standard semiconductor fabrication processes, making process of the Micromirror Array Lens is only dependent on the substrate wafer size. If the size of the lens is less than that of substrate wafer, then fabrication process is the same. Second, different kinds of lenses can be fabricated together. While fabricating the conventional lenses, the curvature of the lens determines the fabrication capability. Thus, only one kind of lens can be fabricated together. While fabricating the Micromirror Array Lenses, many different kinds of the Micromirror Array Lenses can be fabricated together. Third, since the Micromirror Array Lens is an adaptive optical element, the aberration of the optical system can be corrected by introducing the Micromirror Array Lens. Each micromirror can be designed to correct the aberration problem of the optical system. Fourth, mass productivity is a major advantage of the Micromirror Array Lens. Since Micromirror Array Lens is fabricated by using standard semiconductor procedures, the mass production of lenses can be easily achieved. Also, since the Micromirror Array Lens is arranged in a flat surface, the Micromirror Array Lens reduces the size of the optical system and also critically reduces the problems of mounting optics. And last, the fixed focal length Micromirror Array Lens has a great advantage over variable focal length Micromirror Array Lens. Since the structure of the micromirror can be simplified, the fabrication becomes extremely simple. Also the production cost is so low that the fixed focal length Micromirror Array Lens can substitute the conventional lens in the optical systems.
The present invention provides a new simple lens surface forming and fabrication process. By introducing the Micromirror Array Lens with a surface profile shape memory, simple Micromirror Array Lens can be fabricated without loosing the great advantages of the Micromirror Array Lens.